1. Field of the Invention
The present invention relates to transmitting information across an interface. More specifically, the present invention relates to transmitting both AC and DC information across a high bandwidth magnetic interface with low distortion.
2. Background of the Invention
Many current electronic systems incorporate expensive or sensitive electrical components. Because electrical energy is often generated or transmitted at high voltages, the power supplies to these electronic systems must be carefully designed. Power supply design must ensure that the electrical system being supplied with power is not exposed to excessive voltages or currents. In order to isolate power supplies from electrical equipment, many methods have been employed. These methods typically involve control systems or signal transfer methods.
In one method, the power supplies have been electrically isolated from electronic equipment. This has been done using, for example, optical isolation or magnetic isolation. Optical isolation is desirable because of its simplicity. However, the inherent parametric shifting, especially in high radiation environments, often makes this method impossible to utilize. Additionally, optical isolators are typically bandwidth limited to between 10 to 20 KHz.
One type of magnetic isolation method employs magnetic sensors that have an AC signal applied to a winding that is modulated. The resulting signal is magnetically coupled to a winding where the waveform is conditioned by a circuit that is responsible for decoding the modulated signal. Magnetic isolation is ideal for many situations because it can compensate for parametric shifts and high radiation effects with the proper selection of support circuitry. However, magnetic isolation also has disadvantages. The modulation circuitry can be complex, which increases the number of components that are necessary. In addition, the demodulation of a signal is typically subject to non-linearities, which is undesirable in control loop systems.
Another type of magnetically coupled signal transfer involves a self-oscillating, saturating, magnetic-transistor circuit passing information from DC to the MHz region. The nature of these self oscillating circuits is to produce a high duty cycle push-pull action across a transformer winding. During the “on-time,” in the linear region (before the transformer saturates), information is passed from primary to secondary by conventional transformer coupling. In this method, signals that are transferred during this “on time” are only bandwidth limited by series parasitic elements. Therefore, this portion of the circuit can be considered “high bandwidth.” The portion of time involved in saturation does not pass information from primary to secondary. In fact, this moment in time produces the noise that needs to be filtered out of the desired signal. Although this circuit is very effective, it requires very specialized core material with square loop characteristics. This circuit also requires dual power supplies, with at least one of the power supplies requiring two quadrant operation. This type of sensor is utilized in, for example, the PSDU Battery module—A2100M power subsystem.
A continuing need exists for an apparatus for providing an isolated signal interface in a power converted circuit.